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    <title>Document</title>
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<script>
    // String  Boolean null undefined   +  Number

    // null 和 数字 => 先转数字再运算 
    // null => 0 
   

    var a = null;
    var b = 3;
    console.log(a + b); // 3
    console.log(a - b); // -3
    console.log(a * b); // 0
    console.log(a / b); // 0
    console.log(a % b); // 0

    // 1(被除数) / 3(除数) = 0(商) ... 1(余数)

    




</script>
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